1. Field of the Invention
The present invention generally relates to an inkjet ink, a polyamic acid composition for forming a layer of insulator film, for example, in manufacturing electronic components, a polyimide film formed by the composition, a film substrate formed with the polyimide film, and an electronic component having the film substrate.
2. Description of Related Art
Polyimide is a material widely used in the field of electronic communication due to excellent thermal resistance and electric insulation (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). When polyimide is used to form a film with desired patterns, the patterns are generally formed by etching or using photosensitive polyimide in prior art. In recent years, methods for forming the film with desired patterns by utilizing inkjet are under development.
Although various inkjet inks (see, for example, Patent Document 4, and Patent Document 5) are set forth, when preparing a polyimide system inkjet ink, the durability of inkjet head or the precision of jetting is decreased because the solvent contained in the ink composition is limited to an amide solvent, such as N-methyl-2-pyrrolidone, etc. Especially, when a flexible substrate is used, the problems on flexibility (a property for measuring whether the flexible substrate or the circuit thereon is curved or broken off when the flexible substrate is erected with two ends being grasped and alternatively moved upward and downward, also referred to as sliding characteristics) are frequently occurred; thus, a polyimide film having excellent flexibility is preferred.
[Patent Document 1] Japanese Laid-Open Publication No. 2000-039714
[Patent Document 2] Japanese Laid-Open Publication No. 2003-238683
[Patent Document 3] Japanese Laid-Open Publication No. 2004-094118
[Patent Document 4] Japanese Laid-Open Publication No. 2003-213165
[Patent Document 5] Japanese Laid-Open Publication No. 2006-131730